Sajanikumari Sadasivan

Synthesis and shape modification of organo-functionalised silica nanoparticles with ordered mesostructured interiors

Organo-functionalised MCM-41 nanoparticles have been prepared by a dilution/neutralisation method involving the surfactant-templated co-condensation of 3-aminopropyltriethoxysilane, allyltriethoxysilane or 3-mercaptopropyltriethoxysilane with tetraethoxysilane under alkaline conditions. The presence of covalently coupled organic groups within the hexagonally ordered silica mesophase was confirmed by solid-state 13C and 29Si MAS NMR spectroscopy. TEM studies show that amine- and allyl-functionalised nanoparticles are single-domain oblate ellipsoidal crystals, in which the cylindrical micelles are aligned parallel to the morphological minor axis. In contrast, the thiol-functionalised nanoparticles were synthesised in the form of nanofilaments elongated specifically along the channel direction of the MCM-41 hexagonal mesostructure. A mechanism is proposed in which changes in the nanoparticle morphology are attributed predominantly to an increase in surface charge associated with the anionic mercaptopropyl groups that inhibits the side-on attachment of silica–surfactant micelles to partially ordered primary nanoclusters. In contrast, nanoparticles with neutral side chains, such as amino and allyl moieties, as well as unfunctionalised MCM-41, develop by side-on attachment to radially arranged defect sites of a modulated hexagonal mesophase associated with the oblate ellipsoidal morphology.

Novel protein-inorganic nanoparticles prepared by inorganic replication of self-assembled clathrin cages and triskelia

Clathrin nanocages are constructed through spatially extended contacts that arise between helix hairpin motifs of overlapping triskelia, and as such represent an unusual protein nanostructure for the structural templating of novel types of bioinorganic constructs. Solid hybrid nanoparticles comprising a single gel-embedded polyhedral protein (clathrin) cage were produced by template-directed condensation of polycationic clusters of aminopropyl-functionalized magnesium phyllosilicate or oligomers of aminopropyl-functionalized silica. Alternatively, tripodal or hollow spheroidal clathrin–CdS constructs decorated with arrays of semiconductor nanoparticles were obtained by binding Cd(II) ions to individual triskelia or preformed cages, respectively, followed by reaction with sodium sulfide. Replication of the protein superstructures is facilitated by electrostatic interactions, and is accomplished without loss of secondary structure.

Fabrication of functional bioinorganic nanoconstructs by polymer-silica wrapping of individual myoglobin molecules

Discrete core-shell hybrid nanoparticles comprising individual met-myoglobin (met-Mb) molecules incarcerated within an ultrathin polymer/silica shell were prepared without loss of biofunctionality by a facile self-assembly procedure. Solubilisation of met-Mb in cyclohexane in the near-absence of water was achieved by wrapping individual protein molecules in the amphiphilic triblock copolymer poly(ethylene-oxide)19-poly(propylene-oxide)69-poly(ethylene-oxide)19 (EO19-PO69-EO19, P123). Addition of tetramethoxysilane to the met-Mb/P123 conjugates in cyclohexane produced discrete nanoparticles that contained protein, polymer and silica, and which were 3-5.5 nm in size, consistent with the entrapment of single molecules of met-Mb. The hybrid nanoconstructs were isolated and re-dispersed in water without loss of secondary structure, and remained functionally active with respect to redox reactions and CO and O2 ligand binding at the porphyrin metallocentre. The incarcerated met-Mb biomolecules showed enhanced thermal stability up to a temperature of around 85 °C. These properties, along with the high biocompatibility of silica and P123, suggest that the silicified protein-polymer constructs could be utilised as functional nanoscale components in bionanotechnology.